1. Field of the Invention
The present invention relates to an ultrasonic system for measuring a moving speed of a material in a medium, or a flowing speed of a liquid by making use of the Doppler effect.
2. Description of the Prior Art
The Doppler effect is available for measuring a moving speed of a material in a medium, or a flowing speed of a liquid. Conventional devices popularly use two thickness-vibration mode transducers; one acts as an input transducer generating an ultrasound vertical to a piezoelectric substrate surface, on which the input transducer is formed; the other acts as an output transducer detecting a reflected ultrasound vertical to a piezoelectric substrate surface, on which the output transducer is formed. Accordingly, it is mechanically difficult to determine a situation of the output transducer to the input transducer. In addition, conventional devices have some problems on measurement accuracy, response time, difficulty in use, and durability. Moreover, conventional devices are easy to be affected by a change in circumstances, such as temperature, pressure, and so on.
An object of the present invention is to provide an ultrasonic moving-speed measuring system with a high sensitivity.
Another object of the present invention is to provide an ultrasonic moving-speed measuring system capable of operating at a high frequency.
Another object of the present invention is to provide an ultrasonic moving-speed measuring system excellent in measurement accuracy, response time, durability, and manufacturing.
Another object of the present invention is to provide an ultrasonic moving-speed measuring system capable of canceling a change in circumstances such as temperature, pressure, and so on.
Another object of the present invention is to provide an ultrasonic moving-speed measuring system capable of low electric power consumption.
A still other object of the present invention is to provide an ultrasonic moving-speed measuring system easy in use and having a small size which is very light in weight and has a simple structure.
According to one aspect of the present invention there is provided an ultrasonic moving-speed measuring system comprising (1) a piezoelectric substrate, (2) a first electrode formed on an upper end surface of the piezoelectric substrate, (3) a second electrode formed on a lower end surface of the piezoelectric substrate, (4) an interdigital transducer formed on the upper end surface of the piezoelectric substrate, and (5) a signal analyzer. The first electrode and the second electrode that is located at the corresponding position with the first electrode form a thickness-vibration mode transducer. The piezoelectric substrate, the thickness-vibration mode transducer, and the interdigital transducer form a transducing assembly.
When an input electric signal with a carrier frequency, approximately equal to the center frequency for operating the thickness-vibration mode transducer, is applied to the thickness-vibration mode transducer, a longitudinal wave is radiated into a medium that is in touch with the bottom of the transducing assembly. If the longitudinal wave is reflected at a material in the medium, a delayed electric signal with a Doppler frequency is detected at the interdigital transducer via a mode conversion from a reflected longitudinal wave to a leaky Lamb wave. A moving speed of the material is sensed at the signal analyzer in terms of a difference between the carrier- and Doppler frequencies.
According to another aspect of the present invention there is provided an interdigital transducer having a dispersive electrode-pattern.
According to another aspect of the present invention there is provided an interdigital transducer having an arch-shaped electrode-pattern with a concentric center at a coincident situation with the center of the first electrode.
According to another aspect of the present invention there is provided a counter electrode formed on the lower end surface of the piezoelectric substrate and located at the corresponding position with the interdigital transducer.
According to another aspect of the present invention there is provided a signal generator generating an input electric signal Ei (i=1, 2, . . . , or n) with a carrier frequency F0i (i=1, 2, . . . , or n) in response to a distance Di (i=1, 2, . . . , or n), respectively, between the transducing assembly and the material, in order to make the interdigital transducer n) via a mode conversion from a reflected longitudinal wave with a reflection angle xcex1i (i=1, 2, . . . , or n) to a leaky Lamb wave.
According to another aspect of the present invention there is provided a first electrode made of two comb-shaped electrodes making together an interdigital arrangement. In this time, the ratio of the interdigital periodicity of the interdigital arrangement to the thickness of the piezoelectric substrate is smaller than five times the ratio of the longitudinal wave velocity in the medium to the leaky Lamb wave velocity in the piezoelectric substrate.
According to another aspect of the present invention there is provided a nonpiezoelectric film, with which the bottom of the transducing assembly is covered.
According to another aspect of the present invention there is provided a piezoelectric substrate made of a piezoelectric ceramic thin plate. In this time, the polarization axis thereof is parallel to the thickness direction thereof.
According to another aspect of the present invention there is provided a piezoelectric substrate made of a piezoelectric polymer film.
According to another aspect of the present invention there is provided a piezoelectric substrate made of a piezoelectric single crystal.
According to another aspect of the present invention there is provided an ultrasonic moving-speed measuring system comprising (1) a piezoelectric substrate, (2) a first interdigital transducer formed on an upper end surface of the piezoelectric substrate, (3) a second interdigital transducer having the same electrode pattern as the first interdigital transducer and formed on the upper end surface of the piezoelectric substrate, (4) a first electrode formed on the upper end surface of the piezoelectric substrate and located between the first- and second interdigital transducers, a second electrode formed on a lower end surface of the piezoelectric substrate and located at the corresponding position with the first electrode, and a signal analyzer. The first- and second electrodes form a thickness-vibration mode transducer. The piezoelectric substrate, the thickness-vibration mode transducer, and the first- and second interdigital transducers form a transducing assembly.
When an input electric signal with a carrier frequency, approximately equal to the center frequency for operating the thickness-vibration mode transducer, is applied to the thickness-vibration mode transducer, a longitudinal wave is radiated into a medium that is in touch with the bottom of the transducing assembly. If the longitudinal wave is reflected at a material in the medium, a first delayed electric signal with a first Doppler frequency is detected at the first interdigital transducer via a mode conversion from a first reflected longitudinal wave to a first leaky Lamb wave, and at the same time, a second delayed electric signal with a second Doppler frequency is detected at the second interdigital transducer via a mode conversion from a second reflected longitudinal wave to a second leaky Lamb wave. A moving direction and a moving speed of the material is sensed at the signal analyzer in terms of a difference between the carrier frequency and a larger one of the first- and second Doppler frequencies.
According to another aspect of the present invention there are provided first- and second interdigital transducers, wherein an intersecting line on each finger-center of the finger overlap-zone of the first interdigital transducer and that of the second interdigital transducer overlap each other.
According to another aspect of the present invention there are provided first- and second interdigital transducers having a dispersive electrode-pattern, respectively.
According to another aspect of the present invention there are provided first- and second interdigital transducers having an arch-shaped electrode-pattern, respectively, and making a pair with a concentric center at a coincident situation with the center of the first electrode.
According to another aspect of the present invention there are provided first- and second counter electrodes. The first counter electrode is formed on the lower end surface of the piezoelectric substrate and located at the corresponding position with the first interdigital transducer. The second counter electrode is formed on the lower end surface of the piezoelectric substrate and located at the corresponding position with the second interdigital transducer.
According to another aspect of the present invention there is provided a signal generator generating an input electric signal Ei (i=1, 2, . . . , or n) with a carrier frequency F0i (i=1, 2, . . . , or n) in response to a distance Di (i=1, 2, . . . , or n), respectively, between the transducing assembly and the material. The use of such the signal generator makes the first interdigital transducer detect a first delayed electric signal with a first Doppler frequency Ffi (i=1, 2, . . . , or n) via a mode conversion from a first reflected longitudinal wave with a reflection angle xcex1i (i=1, 2, . . . , or n) to a first leaky Lamb wave, and at the same time, makes the second interdigital transducer detect a second delayed electric signal with a second Doppler frequency Fsi (i=1, 2, . . . , or n) via a mode conversion from a second reflected longitudinal wave with the reflection angle xcex1i to a second leaky Lamb wave.
According to another aspect of the present invention there is provided an ultrasonic moving-speed measuring system comprising (1) a piezoelectric substrate, (2) a first interdigital transducer, (3) a second interdigital transducer, (4) a third interdigital transducer, (5) a first electrode formed on the upper end surface of the piezoelectric substrate, (6) a second electrode formed on a lower end surface of the piezoelectric substrate, and (7) a signal analyzer. The first-, second-, and third interdigital transducers have the same electrode patterns as one another, and are formed on the upper end surface of the piezoelectric substrate such that they together make a triangle. The first electrode is formed among the first-, second-, and third interdigital transducers on the upper end surface of the piezoelectric substrate. The second electrode formed on the lower end surface of the piezoelectric substrate is located at the corresponding position with the first electrode. The first- and second electrodes form a thickness-vibration mode transducer. The piezoelectric substrate, the thickness-vibration mode transducer, and the first-, second-, and third interdigital transducers form a transducing assembly.
When an input electric signal with a carrier frequency, in a frequency band-width of xc2x16 dB from the center frequency for operating the thickness-vibration mode transducer, is applied to the thickness-vibration mode transducer, a longitudinal wave is radiated into a medium that is in touch with the bottom of the transducing assembly. If the longitudinal wave is reflected at a material in the medium, a first delayed electric signal with a first Doppler frequency is detected at the first interdigital transducer via a mode conversion from a first reflected longitudinal wave to a first leaky Lamb wave, and a second delayed electric signal with a second Doppler frequency is detected at the second interdigital transducer via a mode conversion from a second reflected longitudinal wave to a second leaky Lamb wave, and then a third delayed electric signal with a third Doppler frequency is detected at the third interdigital transducer via a mode conversion from a third reflected longitudinal wave to a third leaky Lamb wave. A moving direction and a moving speed of the material is sensed at the signal analyzer in terms of a combination of a first difference between the carrier frequency and the first Doppler frequency, a second difference between the carrier frequency and the second Doppler frequency, and a third difference between the carrier frequency and the third Doppler frequency.
According to another aspect of the present invention there are provided first-, second-, and third interdigital transducers, wherein a first intersecting line on each finger-center of the finger overlap-zone of the first interdigital transducer, a second intersecting line on each finger-center of the finger overlap-zone of the second interdigital transducer, and a third intersecting line on each finger-center of the finger overlap-zone of the third interdigital transducer meet one another at the center of the first electrode.
According to another aspect of the present invention there are provided first-, second-, and third interdigital transducers having a dispersive electrode-pattern, respectively.
According to another aspect of the present invention there are provided first-, second-, and third interdigital transducers having an arch-shaped electrode-pattern, respectively, and making a set with a concentric center at a coincident situation with the center of the first electrode.
According to other aspect of the present invention there are provided first-, second-, and third counter electrodes. The first counter electrode is formed on the lower end surface of the piezoelectric substrate and located at the corresponding position with the first interdigital transducer. The second counter electrode is formed on the lower end surface of the piezoelectric substrate and located at the corresponding position with the second interdigital transducer. The third counter electrode is formed on the lower end surface of the piezoelectric substrate and located at the corresponding position with the third interdigital transducer.
According to a further aspect of the present invention there is provided a signal generator generating an input electric signal Ei (i=1, 2, . . . , or n) with a carrier frequency F0i (i=1, 2, . . . , or n) in response to a distance Di (i=1, 2, . . . , or n), respectively, between the transducing assembly and the material. The use of such the signal generator makes the first interdigital transducer detect a first delayed electric signal with a first Doppler frequency Ffi (i=1, 2, . . . , or n) via a mode conversion from a first reflected longitudinal wave with a reflection angle xcex1i (i=1, 2, . . . , or n) to a first leaky Lamb wave, and makes the second interdigital transducer detect a second delayed electric signal with a second Doppler frequency Fsi (i=1, 2, . . . , or n) via a mode conversion from a second reflected longitudinal wave with the reflection angle xcex1i to a second leaky Lamb wave, and then, makes the third interdigital transducer detect a third delayed electric signal with a third Doppler frequency Fti (i=1, 2, . . . , or n) via a mode conversion from a third reflected longitudinal wave with the reflection angle xcex1i to a third leaky Lamb wave.